INFORMATION TO USERS
This dissertation was produced from a microfilm copy of the original document. While the most advanced technological means to photograph and reproduce this document have been used, the quality is heavily dependent upon the quality of the original submitted.
The following explanation of techniques is provided to help you understand markings or patterns which may appear on this reproduction.
1. The sign or "target" for pages apparently lacking from the document photographed is "Missing Page(s)". If it was possible to obtain the missing page(s) or section, they are spliced into the film along with adjacent pages. This may have necessitated cutting thru an image and duplicating adjacent pages to insure you complete continuity.
2. When an image on the film is obliterated with a large round black mark, it is an indication that the photographer suspected that the copy may have moved during exposure and thus cause a blurred image. You will find a good image of the page in the adjacent frame.
3. When a map, drawing or chart, etc., was part of the material being photographed the photographer followed a definite method in "sectioning" the material. It is customary to begin photoing at the upper left hand corner of a large sheet and to continue photoing from left to right in equal sections with a small overlap. If necessary, sectioning is continued again — beginning below the first row and continuing on until complete.
4. The majority of users indicate that the textual content is of greatest value, however, a somewhat higher quality reproduction could be made from "photographs" if essential to the understanding of the dissertation. Silver prints of "photographs" may be ordered at additional charge by writing the Order Department, giving the catalog number, title, author and specific pages you wish reproduced.
University Microfilms 300 North Zeeb Road Ann Arbor, Michigan 48106 A Xerox Education Company 73-4939 CONANT, Sheila, 1945- VISUAL AND ACOUSTIC COMMUNICATION IN THE BLUE JAY, Cyàriocittà cristata (Aves, Corvidae). The University of Oklahoma, Ph.D., 1972 Zoology
University Microfilms, A XEROKCompany, Ann Arbor, Michigan
THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED. THE UNIVERSITY OF OKLAHOMA
GRADUATE COLLEGE
VISUAL AND ACOUSTIC COMMUNICATION IN THE BLUE JAY, Cyanocitta cristata (Aves, Corvidae)
A DISSERTATION
SUBMITTED TO THE GRADUATE FACULTY
in partial fulfillment of the requirements for the
degree of
DOCTOR OF PHILOSOPHY
BY
SHEILA CONANT
Norman, Oklahoma
1972 VISUAL AND ACOUSTIC COMMUNICATION IN THE BLUE JAY,
Cyanocitta cristata (Aves, Corvidae)
APPROVED BY
DISSERTATION COMMITTEE PLEASE NOTE;
Some pages may have
indistinct print.
Filmed as received.
University Microfilms, A Xerox Education Company ACKNOWLEDGEMENTS
I would like to thank my advisor, Dr. Charles C.
Carpenter for his guidance and encouragement throughout the project, and for providing space and equipment for me in his laboratory. Thanks are also due to my committee members
Drs. Harley P. Brown, Gary D. Schnell and Paul G. Risser for reading and criticizing this manuscript. My graduate work at the University of Oklahoma has
been supported by a National Science Foundation Traineeship
awarded to me by the Department of Zoology. Mrs. Marjorie
Bradley, Assistant to the Dean of the Graduate College, has
been most helpful in administering the research funds from
the traineeship. Friends too numerous to name have been helpful with
many different parts of the project. I am especially indebted to 25 patient, colorful, and
endearing Blue Jays that were most cooperative research sub
je c ts .
I l l TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS...... i ü
LIST OF TABLES...... v LIST OF ILLUSTRATIONS...... v i
Chapter I . INTRODUCTION...... 1
I I . MATERIALS AND METHODS...... 3 Acquisition and Maintenance of Birds...... 3 Observation—Methods and Equipment...... ^
III. VISUAL DISPLAYS AND POSTURES...... 6
Introduction...... 6 Components of Visual Signals...... 6 Postures and Displays ...... 9
IV. VOCALIZATIONS...... 65 Introduction...... 65 Vocalization Parameters ...... 65 Vocalizations ...... 67
V. DISCUSSION AND CONCLUSIONS...... 1^0
Origin and Significance of Postures and D isp la y s...... 140 Structure, Function and Evolution of Acoustic Signals...... 1^6
VI. SUMMARY...... 156
LITERATURE CITED...... 159
APPENDIX...... 163
iv LIST OF TABLES
Table Page
1 . Per cent of selected vocalizations given with each of the three simple bobbing types ...... 38 2. Physical characteristics of calls in the harmonic spectra group ...... 110
3. Postures and functions associated with calls in the harmonic spectra group ...... 112
h. Physical characteristics of the pumphandle c a l l s ...... 122
5. Postures and functions associated with the pumphandle calls ...... 123
6. Physical characteristics of theclick calls . . . 136
7. Postures and functions associated with the click calls ...... 138
v LIST OF ILLUSTRATIONS
Figure Page 1 . Neutral posture ...... 12 2. Sleeping ...... 1^ 3 . Heat conserving posture ...... I 6
k-. Investigatory posture ...... 19
5. Mild aggression ...... 22
6 . Intense aggression ...... 25
7 . The a g g r essiv e en co u n ter...... 27
8. F ig h tin g ...... 30 9. Simple bobbing ...... 3^ 10. Courtship bobbing ...... ^1
11. Courtship bobbing ...... ^3
12. Courtship bobbing ...... 4-5
13 . Avoidance posture ...... 4-7
14. The n e s tlin g alarm f r e e z e ...... 50
15. Appeasement posture ...... 53
16 . Courtship feeding solicitation...... 56
17* Courtship feed in g ...... 59
18. Precopulatory display and copulatory position . .63
19* The D istr e ss C all (DC)...... 71
v i Figure Page
20. The Alarm C all (AC)...... 7*+
21. The Flock Contact Call (FC) ...... 77 22. The number of Flock Contact Calls per hour throughout the year ...... 79 23 . The Flock Contact Call of young Blue Jays (YFC). 82
2^-. The Food-begging Call of young Blue Jays, Type 1(YFB1) ...... 85 2 5. The Food-begging Call of young Blue Jays, Type 2(YFB2) ...... 87
26. The Food-begging Call of young Blue Jays, Type 3 (YFB3)...... 90 2 7. The Food-begging Call of young Blue Jays, Type 4 (YFB^-)...... 93
2 8. The Begging Keu C all (BK) ...... 96
29. The Soft Keu C all ( S K ) ...... 98
3 0 . The Loud Keu C all (L K ) ...... 101
31 . The Crow C all ( C C )...... 10>+ 32 . The Meow Call- (M C )...... 107
33 ' The meow of a c a t ...... 109
3^. The B ell Song ( B S ) ...... 115
35 . The B ell Song of young Blue Jays (Y B S ) ...... I I 8 36. The Wheedle B ell Song (WBS) ...... 120
37. The Rolling Click Call (RC) ...... 125 38. The Descending Whistle (DW)...... 129
39. The Growl (G R )...... 131 ^0. The T rip le Descending W histle (TDW)...... 13*+
V l l VISUAL AND ACOUSTIC COMMUNICATION IN THE BLUE JAY,
Cyanocitta cristata (Aves, Corvidae)
CHAPTER I
INTRODUCTION
The Blue Jay, one of the more familiar and widely distributed North American corvids, exhibits a wide variety of distinct acoustic and visual communication signals. Hardy
(1961) made a rather thorough study of the life history of the Blue Jay, including visual and vocal communication, but he did not investigate communication in depth. Edwards
(1971) investigated the ontogeny of vocalization in the Blue Jay, describing the development of various calls, ascribing fu n ctio n s to some. A number of life history and behavior studies on other New World jays have been made, the most extensive of which are: Amadon (19^^)» Florida Scrub Jay (Aphelocoma coerulescens coerulescens); Brown (19&3&, 1963b, 1964), Mexican (A. ultramarina arizonae) and Steller's jays
(Cyanocitta stelleri); and Gross (19^9) Mexican Jay. All of these stu d ie s include a t l e a s t some observations and comments on communication signals of the various species.
1 2
Blue Jays lend themselves well to laboratory studies; they are easily raised, maintained and observed, and they exhibit a rich repertoire of behavior patterns. They adapt well to captivity and, apparently, show little behavioral distortion, other than a tendency to be "tame" or unafraid of humans, resulting from the necessary constraints of captive e x iste n ce ,
I decided to study Blue Jays because their repertoire of communication signals is large and has not been well-described. They are easily observed in the field and are excellent subjects for studies in captivity. My objectives in the study were to describe the physical characteristics of acoustic and visual displays and to determine their biological significance. CHA.PTER I I
MATERIALS AND METHODS
Acquisition and Maintenance of Birds
The majority of the data presented here were gathered during observations of 25 captive, hand-raised birds. All of the birds were collected from various locations within
Cleveland County, Oklahoma. They were acquired from nests at ages ranging from one to five weeks. Six birds were collected in the spring of 1969, and, in 1971, 19 more birds were taken during the spring and summer months.
From May, 1969, until December, 1970, the birds were kept at my home in an aviary with a 6 x 8 x 12 ft indoor flight and a 12 x 1*+ x 16 ft outdoor flight. In December,
1970, the birds were moved to the Animal Behavior Laboratory on the North Campus of the University of Oklahoma, where they were kept in an aviary with an 8 x 12 x 20 ft indoor flight and a 15 X 30 X 30 ft outdoor flight. No behavioral differences that might have been attributed to the move were apparent. Occasionally, individual birds or pairs were placed in other, smaller aviaries for special observation. If
Both nestling and adult diets contained varying amounts of the following items: fresh and dried fruits and vegetables, hard-boiled eggs with shells, fresh meat, cracked corn, sunflower seeds, raw peanuts, honey, graham crackers, Purina Pigeon Checkers, Purina Dog Chow, Prunty's Mockingbird
Food, Prunty's Nestling (Egg) Food, and vitamin supplements.
Some live insects were available during the warmer months. Limecake, pumice blocks, and fresh water for drinking and bathing were available at all times.
All birds were banded with both U.S. Fish and
Wildlife Service aluminum bands and colored plastic bands for individual recognition.
Observation—Methods and Equipment
Vocalizations were recorded with a Uher ^-000 Report-L portable tape recorder (frequency response )+0 to 20,000 Hz)
and a Uher omnidirectional microphone (frequency response
70 to lH-,000 Hz). Sound analyses were made with both a Tektronix type 502A Dual Beam Oscilloscope and a Kay
Sonagraph, model 1029-A. On the Sonagraph the frequency band
s e ttin g used fo r most analyses was 80 to 8,000 Hz. The wide
band pass filter, with a frequency resolution of 3 OO Hz was
used for temporal resolution, and the narrow band pass
filter, with a frequency resolution of >+5 Hz was used for
frequency resolution.
Motion pictures were made with a model H-I 6 Bolex
16 mm movie camera and a 17-85 ®m Pan Cinor zoom lens. 5 Motion analyses of disp lay s recorded on film were made by projecting film with a Bell and Howell Model 173 Time and
Motion Study Projector. An Esterline Angus 20-channel Event Recorder, coded in series for about 50 behavior patterns (including both visual and vocal displays), was used to record data during observation periods. Because the birds were "unafraid" of humans, it was not necessary to use a blind for observation. Most observations were made within 10 m of the cage or even inside it. Binoculars (7 x 35) were used to facilitate identification of individual birds.
Field observations and experiments were made frequently throughout the course of the study. Data from field observations allowed me to compare the behavior of
captive and wild birds, as well as to gather data under field
conditions on the function of displays. CHAPTER I I I
VISUAL DISPLAYS AND POSTURES
Introduction
Blue Jays exhibit at least 20 distinct visual displays or postures. The function of a given posture or display is determined by the context in which it is given, and involves fixed or moving aspects of "facial expression," head position, body position and piloerection. Movement in general, as well as movement of specific, often visually conspicuous, parts of the body or plumage, serves, at least in part, to give visual emphasis to displays. In many cases movement functions only to emphasize a visual display without changing its meaning, just as an increase in volume might emphasize an acoustic signal.
Components of Visual Signals
The components of postures and displays that function
as communication signals in the Blue Jay may be grouped into
three categories: 1) "facial expression" and head position,
2) body position, 3) movement and position of plumage. Each
category has several variations, each of which is graded, or continuously variable.
6 7 1. "Facial expression" and head position may be modified in several ways. The position of the crest varies from erect to appressed, the position of the mandibles varies from open to closed, and the position of the head may be below, at the same level as, or above the body axis. The direction of point of the bill is important, but highly v a ria b le . 2. Body positions vary, but can be placed in several groups. The body is considered crouched when the ankle joint is bent so that an angle of less than 90° is formed by the tibiotarsus and the tarsometatarsus. When the body is in the neutral position, as during periods of mild activity or inactivity, this angle approximates 90°. In the "tiptoed" position the angle is greater than 90°. The orientation of the body with respect to the horizontal varies among and within displays. The body is sometimes rotated from the neutral position (body at an angle
of about 49° with th,e horizontal) so that the head and upper
torso move vertically up or down. Extremes of this position
occur when the body is held nearly perpendicular to the perch
or when the head is lowered to a point where it is below the perch. The point of rotation of the body may be either the
ankle or knee joint. Occasionally, during a display, the feet leave the
perch entirely, although the bird does not initiate flight or
spread its wings, but, instead, returns to the perch. This 8 type of body movement is usually associated with intense excitement. Finally, the bird may be in flight at some point during a display. 3 . The movement and position of plumage is an important component of visual displays. Different degrees of pilop ction are observed within and among displays and to have communicative significance. Morris (1956) has described four degrees of piloerection, and I will adhere to his descriptions when discussing piloerection in this paper. They are as follows : 1) sleeked, the plumage is actively depressed against the body; 2 ) relaxed, the plumage is neither actively depressed nor erected; 3 ) fluffed, the plum^^e is partially erected and the feathers remain in contact with each other; 4) ruffled, the plumage is fully erected, and the feathers no longer remain in contact with each other.
The wings and tail are often moved during displays;
they may be fluttered, flicked or held stationary. Both the wings and tail may be fanned (i.e., moved from the closed to
the open position or to some point between these extremes)
while they are fluttered or flicked. If the wings and tail
are held stationary during a display they may be held at any
point from closed to fully fanned. The Blue Jay is a strikingly marked bird and some
attributes of its coloring appear to be important in visual
displays. The black facial mask and collar probably give
added visual emphasis to displays, especially to those 9 displays involving movement of the head as well as those in which the displaying bird is within several meters of the animal to which the display is directed. Courtship and agonistic postures and displays often involve various degrees of piloerection whereby dark areas of the plumage are increased in area. The white and black wing and tail bars are conspicuous during movement. Fluttering, flicking and fanning of the wings and tail make these bars, particularly the white ones, quite obvious.
Postures and Displays Visual communication signals may be placed in three groups on the basis of functional and physical sim ilarities.
The first group of postures, which do not appear to function as communicative signals, includes those assumed during maintenance activities. They are characterized by relaxed or fluffed plumage, neutral body position, appressed wings and
closed tail. The second group is characterized functionally
as primarily agonistic and is associated with erection of
body plumage and, especially, head plumage and abrupt movements, if any, of wings and tail. The last group of displays functions as submissive or solicitative signals, and
is associated with sleeking of both head and body plumage and
fluttering type movements of the wings and tail if these appendages are moved at all. Each of these types will be discussed below. 10 Maintenance Postures
Neutral posture (Fig. 1). This posture is assumed by the bird during periods of mild activity (not including long rest periods or sleeping), for example, as a bird forages on the ground or up in the vegetation. In neutral posture, the crest and plumage are relaxed; the bill is closed and pointed forward. The body is in neutral orientation to the horizontal, and the wings and tail are fully closed. Ofcourse, as the bird moves, aspects
of the posture are necessarily modified by the nature of the
activity. For example, if the bird is foraging it moves
about actively looking for and picking up food items. Sleeping (Fig. 2). While a Blue Jay is asleep, the
crest is relaxed and the body plumage is usually fluffed.
The body is crouched, and the bird may rest its full weight
on only one foot. The head is usually turned backward with the bill nearly parallel to the body axis and tucked behind
the wing. At times the head is merely lowered between the
shoulders, giving the bird a hunched appearance. This
hunched appearance is often seen during midafternoon rest
periods. During daytime rest periods, the bill is never tucked behind the wing; whereas, during nocturnal sleeping the head is turned back and the bill tucked behind the wing
more often than it is hunched with the bill pointing forward.
Thermoregulatory postures
Heat conserving posture (Fig. 3)* Birds often assume Figure 1. Neutral posture. 12 Figure 2. Sleeping. 1^
I' é F igure 3 . Heat conserving posture. 16 17 this posture, which is characterized by fluffing of all body and head plumage, on cold days when they are inactive.
According to Morris (1956) feathers in the fluffed position
(feathers erect but still in contact with one another) facilitate heat conservation because the entrapped air spaces between them have reached maximum size, thus providing the greatest insulation possible.
Cooling posture. On very warm days, inactive jays often perch with their feathers ruffled (fully erect and no longer in contact with one another). Morris (1956) contends
that ruffling of feathers increases heat loss because
entrapped air spaces and, concomitantly, insulation are lost when the feathers lose contact. A ruffled, inactive Blue Jay
would look much like the one illustrated in Fig. 3, except that it would have a ragged outline.
Bathing. During both water bathing and sunbathing the feathers are ruffled and the wings and tail fully fanned.
Ruffling of feathers during bathing probably facilitates wetting (by water) or warming (by the sun) of both the feathers
and the skin. Preening, which always follows water bathing and
occasionally follows sunbathing, is performed with the feathers
ruffled. Ruffling of the feathers immediately around the cloaca occurs during defecation.
Agonistic Postures and Displays
Investigatory posture (Fig. 4-). This posture, first described by Hardy (1961), is assumed by a Blue Jay Figure h. Investigatory posture. 19 20 investigating strange objects that may or may not pose a threat. In this posture, the bill is closed and pointed forward, the crest is fluffed, and the head is held above the tail and body axis. The body is held in neutral or slightly "tiptoed" position with body plumage fluffed. The wings are appressed and the tail is slightly fanned. Alert posture. The alert posture is quite similar to investigatory posture except that the wings and tail are occasionally flicked. If the bird is in motion during investigatory posture or alert posture, movements are usually stiff and jerky. The bird is easily startled and appears ready for instantaneous flight.
Aggressive Postures and Displays The characteristics of aggressive postures of Blue
Jays vary with the intensity of aggression shown by the
displaying bird or birds. Although this variation is
continuous, it is possible to characterize the postures
observed at the extremes (mild to intense) of aggression.
Mild aggression (Fig. 5)* Aggressive encounters of
low intensity occurred frequently among the captive jays. An
example of this is the supplanting of one bird by another on
a perch or at a feeding area. The posture of the aggressor
in such encounters is easily recognized. The bill is closed and pointed forward and the crest is fluffed. The head is usually held above the tail and body axis while the body
itself is slightly crouched. The body plumage is sleeked or Figure 5. Mild aggression. 22 23 relaxed, the wings are appressed and the tail is slightly fanned. Intense aggression (Fig. 6). Aggressive encounters of high intensity occurred infrequently in my captive birds except during the breeding season, when they are common. At this time the birds show an increase in the amount of defensive behavior, i.e., "claiming" or "stealing" food, nest material, mates, perching sites, etc. A highly excited, aggressive Blue Jay assumes a characteristic posture. The bill is open and directed at the object of aggression. The crest is fully erect or ruffled, while the position of the head with respect to the body axis varies. The wings and tail are at least partially, and often fully fanned. Sometimes the wings or tail or both are flicked.
In high intensity aggression the degree of piloerection varies considerably. Infrequently, the plumage
is sleeked or even relaxed. Bill snapping may accompany intense aggressive displays.
The aggressive encounter (Fig. 7). Fig. 7 is a
sketch of three Blue Jays (the two shown uppermost are
involved in the encounter) during an aggressive encounter.
Both birds exhibit some of the characteristics of the
aggressive p o stu re . The b ird on th e l e f t e v en tu ally won th is
encounter, which was recorded on film, by supplanting the
other bird. Note the position of the winner's head with
respect to its own body and the body and head of the other Figure 6. Intense aggression. 25 F ig u re 7. The aggressive encounter. 27
I
1 28 bird. Victory in an aggressive encounter can be predicted by noting the position of the winner’s head with respect to the body axis and the head of the opposer. The winner's head nearly always is either horizontal to or below its own body
axis and tail, and below the head of its opponent. There are two other factors that, to some degree,
predispose victory in aggressive encounters. Most important
is the birds' position in the established dominance hierarchy;
the subdominant in an aggressive encounter nearly always loses, presumably by choice. Frequently a bird may supplant
another bird by a "surprise attack." In this case, the
aggressor flies toward or approaches the attacked bird in
such a way that it cannot see the approach. This serves to
startle the attacked bird and, invariably, it is displaced. This kind of approach may permit a bird to win an encounter
over an opponent that is higher in the dominance hierarchy.
Fighting (Fig. 8). On rare occasions, two Blue Jays
will become involved in a fight. Fights usually occur when
one bird refuses to be displaced from a perch or feeding
station, or when there is a dispute over possession of a food item. When two birds are fighting they are in hovering
flight, face to face with body plumage ruffled, clawing at
each other. After a few bouts of clawing and hovering, one
bird chases the other until it escapes and is a good distance from the chaser or until the chased bird is cornered and gives the appeasement posture (Fig. l4), which will be Figure 8• Fighting 30
: 31 discussed later. Body contact during fights is infrequent.
Simple bobbing (Fig. 9). This display is given in both agonistic and sexual contexts, and is the most frequent display given by Blue Jays. The simple bob, which is rarely
observed unaccompanied by vocalization, functions primarily to add visual emphasis to vocal signals. Field observations reveal that when bobbing involves communication among individuals at some distance (over about 50 m) there are nearly always conspecific observers present and, in my
estimation, their view of the displaying bird is good.
Simple bobbing also accompanies vocalizations given among
groups of birds in close proximity, but it is less
consistently employed in the presence of conspecific observers
at close range than those that are at a distance.
I recorded the number of vocalizations with or without
bobbing displays by jays in the presence of proximate or
distant conspecific observers. Of 308 vocalizations given at
a distance of over 50 m from the observer, 2k6 (80^) were
accompanied by bobbing. Only 189 of 517 vocalizations (37^) given less than 50 m from the observer were accompanied by
bobbing. There is a significantly (X^ = ^ 13 .3 6, P< .005) higher frequency of bobbing associated with vocalizations
involving distance communication than with vocalizations
involving proximate communication.
The hypothesis that bobbing is important in visual communication among birds located some distance from each 32 other is further strengthened by the fact that it never accompanies those vocalizations that involve communication between individuals within 10 m of each other. The food begging call of the young, the courtship feeding or copulation
solicitation call of the adult female are never accompanied by
bobbing. In these cases, exchange of information occurs
between birds that are usually within a meter or so of each
o th er.
F ig . 9 illustrates the movement of the bird during a
simple bob. At the beginning of the display (A, Fig. 9) the
bird is in neutral body position with plumage relaxed, wings
appressed, tail usually closed, and head above body axis and
tail tip. Bobbing is initiated as the bird begins to crouch
and lower the head to a position level with the body axis and
below the t a i l tip (B, F ig. 9)* The bird next returns through
the original neutral position (A, Fig. 9) and then "tiptoes,"
at the same time raising the head above the body axis and
d e fle c tin g the t a i l downward (C, F ig . 9)* At the h eig h t of
the bobbing motion the bill may be directed vertically upward
or it may remain in a horizontal position. In addition, if
the bob is quite deep and/or the bird is excited, one or both
feet may leave the perch at the high point of the bob.
Bobbing is concluded as the bird returns again to the original
neutral position. Occasionally, an additional crouch (B,
Fig. 9) and return to neutral position are added. The depth of the bob varies, becoming proportionately deeper with increased excitement. Figure 9* Simple bobbing 3^
s
IM 35 There are several important characteristics of the simple bob: a) During the simple bob, there is no appreciable horizontal movement on perches or movement from perch to perch, b) Simple bobs are discrete single units; if several bobs are given in a short time period, there is a slight pause between bobs, c) The simple bob is a smooth, continuous movement, d) The plumage is relaxed except for an occasional tail flick, e) Simple bobbing usually involves bending of the ankle joint; it is analogous to a curtsy.
Because there was a gradation in the depth of bobs, I arbitrarily classified simple bobs into three categories:
1. Head bobbing. Some bobs involved movement only of the head and neck. During this type of bobbing there was no fle x io n of the ankle j o in t or downward d e fle c tio n of the tail. This type of bob was given in situations of very low excitement. Vocalizations accompanying this display were often at a relatively low sound level as subjectively judged by the observer.
2. Body bobbing. The majority of simple bobbing falls into this category. This type of bob is one that follows the pattern illustrated in Fig. The entire body is bobbed, the ankle joint is flexed both at the crouched position in the downward movement and at the horizontally elevated "tiptoed" position in the upward movement of the display. In addition, the bill is directed upward and the t a i l is d e fle c te d downward sim ultaneously a t the h eig h t of the bob. 36 3. Exaggerated bobbing. During an exaggerated bob, the displaying bird bobs more deeply than during body bobbing, and, at the height of the bob, one or both feet leave the perch. Both feet may leave and return to the perch simultaneously or one foot may be lifted from and returned to the perch slightly out of phase with the other. Whether or not the feet move in synchrony does not seem to be communicatively significant.
Preliminary observations suggested that head bobbing, body bobbing, and exaggerated bobbing were associated with low, mild, and high levels of excitement, respectively. To test this, I chose three vocalizations that were consistently associated with bobbing and were themselves characteristic of the arbitrarily designated levels of excitement. I recorded the number of times each bob type was associated with each of the three vocalizations. Data on calls not associated with bobbing were not used in statistical tests for significant association of calls with bob types.
The alarm call is invariably associated with high levels of excitement evoked by such things as the presence of potential predators (cats, etc.). The bell song is most frequently associated with a mild level of excitement. The call is usually territorial, but occasionally functions as an alert signal that serves to call attention to an unusual
object or organism in the aviary. The flock contact call is
given by unexcited birds, or at least by birds that exhibit 37 a very low level of excitement. This call serves as an acoustic mechanism by which flock continuity is maintained.
Table 1 shows the percentage of vocalizations given with each bobbing type during observation periods. The data in Table 1 were put in a 3 % 3 contingency table and submitted to a Chi-square test for non-random
association of vocalizations with bobbing types. It was shown th a t the flo c k c o n ta c t c a ll was a sso c ia te d w ith head
bobbing, the bell song was associated with body bobbing, and
the alarm call was associated with exaggerated bobbing
(x2 = 1358.20, P 4.005).
It seems, then, that the primary functions of simple bobbing are 1) to give visual emphasis to acoustic
communication signals, and 2) to indicate the level of
behavioral excitement of the bird that is bobbing.
Courtship display (Figs. 10, 11 and 12). This is the
principal courtship display of the male Blue Jay, and it is
always accompanied by the courtship vocalization.
Although courtship display is similar to simple
bobbing with respect to the type of vertical movement during
the display, it differs from simple bobbing in a number of important aspects, a) The bird changes location both vertically and horizontally as it displays, b) Courtship
display consists of series of bobs with little or no pause
between individual bobs, c) The bobs in courtship display
are characterized by jerky rather than smooth movements. 38 Table 1.—Per cent of selected vocalizations given with each of the three simple bobbing types
Flock Contact C all B ell Song Alarm, C all (n = ^02) (n = 266) (n = 324) % no. % n o . % n o .
Head bobbing 87.3 351 7.5 20 5.6 18 Body bobbing 5.5 23 87.2 232 12.4 l4 Exaggerated bobbing 7.2 28 5.3 1>+ 82.1 266 39 d) There is considerable piloerection, especially of the feathers on the head and neck, which are ruffled, and the wings and tails are frequently flicked, e) Courtship bobbing does not involve bending of the ankle joint; it is analogous to a bow rather than a curtsy.
Both the degree of piloerection and abruptness of movement characteristic of courtship bobbing visually enhance this display. Head and neck feathers are ruffled, effectively increasing the apparent size of the black facial mask and collar. Flicking of the wings and tail with each separate vertical movement (Fig. 10, A, B; Fig. 11, C. D; Fig. 12, E,
F) serves to flash the white markings on the feathers of these appendages. Because the bird does not bend the ankle joint to effect a crouching position, it appears to be "tall" at all times.
Courtship and agonistic displays in many animals are characterized by movements and changes of body position and shape th a t make the animal appear la rg e r than i t does when not displaying (Hinde, 1966). Both the aggressive postures and the courtship display of the Blue Jay exhibit this phenomenon quite well.
Submissive and Solicitative Postures and Displays Avoidance posture (Fig. 13). When two or more birds are perched at a feeding station there is usually one individual that feeds first and then leaves. The other individual(s) present remain(s) perched at the feeder without Figure 10. Courtship hohhing w Figure 11. Courtship hohhiug
Figure 12. Courtship bobbing. ^5
^ r Figure 13. Avoidance posture (exhibited by bird at left). k7 ^8 feeding, apparently waiting for the dominant(s) to feed and leave. In this situation, the subdominant exhibits what I will call the avoidance posture toward the dominant bird.
This is illustrated in Fig. 13, where the dominant bird is on
the right. The avoiding bird perches with its bill closed,
and its head and bill pointing parallel to or away from the dominant. The crest is relaxed or sleeked, and the head is
above the tail and body axis. Wings are appressed, and the
tail is closed and often deflected downward. At times the
subdominant may lean slightly away from the dominant. Eye
contact is avoided.
The avoided bird need not have assumed an aggressive
posture. Assumption of an aggressive or threat posture under these circumstances would normally result in the flight of the subdominant. Avoidance behavior is strongly influenced
by the position of the individuals in the dominance hierarchy.
This behavior permits two or more birds to be at the feeding
station simultaneously, although the dominant has first
choice of food. This behavior also facilitates conservation
of energy in that the dominant bird does not supplant other
individuals while feeding. If the birds have been without
food for several hours or if the feeder contains an especially
favored food such as peanuts or graham crackers, supplanting
occurs more than avoiding.
Nestling alarm freeze (Fig. 1*+). In response to
mechanical nest disturbance or an alarm call given by an adult Figure iM-. The nestling alarm freeze 50
I 51 Blue Jay, nestling jays assume what I have called the alarm freeze. In this posture the bill is closed and directed upward. The crest and body plumage are sleeked, wings closely appressed to the body, and tail closed. The head is drawn down between the shoulders and the body is fully
crouched and held completely rigid. Unless the nestlings are further disturbed by handling, which may elicit a distress
call, no vocalizations accompany this posture.
Appeasement posture (Fig. 15)> When one bird is
cornered during a fight or chasing bout by another individual
that is higher in the dominance hierarchy, the cornered bird assumes a submissive stance that I have called the
appeasement posture. In appeasement posture the body is held
rigid, with the head and opened bill pointed upward and the
t a i l d e fle cted downward so th a t the b ir d 's body a x is,
including head and tail is nearly perpendicular to the perch.
The bird is fully tiptoed in this posture with body plumage
sleeked and wings closely appressed to the body. While the
cornered bird is in the appeasement posture, the dominant
bird (on the right. Fig. 15) pecks lightly at the exposed
neck and belly of its subdominant, but never enough to inflict
any injury. At some point the head is slightly higher than
the head of the cornered bird. At this point the dominant
pecks at the subdominant's bill or even inserts its bill into the open mouth of the submissive individual.
Some elements of the appeasement posture are similar to other submissive displays of the Blue Jay. Exposure of the Figure 15. Appeasement posture (exhibited by bird at left). 53
% 5^ belly and neck occur during aggressive encounters because the winner of the encounter always has its head lower than the head of the loser and in a position from which it could easily peck at these vulnerable places. The open bill is characteristic of displays of adult females soliciting food or copulation (Figs. 16 and l8) and young birds soliciting food. The rigid, bill-up body position is similar to the stance of nestlings in the alarm freeze (Fig. 14J. Hardy
(1961) has described the postures assumed during conflicts between dominant and subdominant Mexican Jays. They are remarkably similar to the postures and movements of Blue Jays in a dominance conflict.
Courtship feeding solicitation (Fig. I 6). This is characteristically a female display, although it is occasionally given by an adult male. When she is soliciting food from her mate or a courting male, the adult female crouches slightly, fluttering her partly fanned wings and tail. The crest is relaxed or sleeked and the body plumage is relaxed. The head, with slightly open bill is held nearly horizontal to the body axis and below the tail tip. An offering of food or nest material from the female may elicit a very brief courtship feeding solicitation display from the adult male. Courtship feeding solicitation display is always accompanied by the begging "keu" call.
The intensity of courtship feeding solicitation by
the female varies considerably. At times she will follow her Figure 16. Courtship feeding solicitation. 56 57 mate, giving the display with intense begging vocalizations until she is presented with a food item or a piece of nest
material. At other times the male brings items unsolicited, and the female accepts them w ith a minimum of wing
fluttering, crouching and vocalizing. Courtship feeding (Fig. 17). Both courtship feeding
and as well as courtship feeding solicitation are an integral
part of pair formation, nest building, incubation, care of the young, and pair bond maintenance in Blue Jays (Hardy, 1961). Courtship feeding first appears when two birds have
formed a weak pair bond during the courtship activity that
precedes nesting. Before nest building begins, food items are
the only type of material exchanged between members of a pair.
As nest building begins, exchanges of nest material increase
and, at the height of nest building, these outnumber exchanges
of food. During incubation, which is entirely a female
activity, the exchange of food items again increases as the
male feeds his mate while she incubates. Although she
continues to forage for herself during brief absences from the nest, the female receives much of her food from the male.
After the young have hatched, courtship feeding continues,
but at a lower rate, and the female rarely eats the food she
receives from her mate, passing most of it to the young. The
male also brings food directly to the young, although it may
be a day or so before he gives it to them directly, rather
than giving it to the female. Hardy (I 96I) has carefully F ig u re 17. Courtship feeding 59
V 60 described courtship feeding in the Blue Jay and my account does not differ from his. Fig. 17 is a sketch of two birds about to exchange a food item in courtship feed in g . At the moment of exchange, both birds give the begging "keu" call. The female may occasionally present her mate with a food item or piece of nest material. This presentation is rarely solicited by the male, although at the moment of exchange he will give a brief courtship feeding solicitation display along with the "keu" call. At times, an item may be passed back and forth several
times between the pair before it is eaten or taken to the nest. During this "trading" of items there is little
crouching or wing fluttering by either bird, but the begging
"keu" vocalization is quite intense. As Hardy (1961) has pointed out, the behavior patterns
characteristic of courtship feeding are an integral part of
the reproductive cycle from the onset of courtship through
care of the young. I have noted that many of the captive jays
maintained pair bonds during the entire non-breeding season
after they had paired in the spring of 1971* No courtship
display or copulation was observed during this period, but
courtship feeding continued with high frequency and seemed to
be the most important factor in maintaining pair bonds. In
late winter and spring of 1972, birds that had maintained
pair bonds from the spring of 1971 showed very little
courtship display, if any, but continued courtship feeding,
which increased as the breeding season progressed. 61 Nestling and fledgling food begging display. The food begging display of young Blue Jays is quite similar to the courtship feeding solicitation display of the adults.
When begging for food a young Blue Jay almost always holds the bill completely open, exposing its bright pink gape, which provides an additional visual cue or "target" for the adult as it gives food to the young bird. The color of the gape in adults is black, and this color difference, in addition to obvious differences in body size and development of plumage, is a major visual characteristic that distinguishes the food begging display of the young from courtship feeding solicitation by adults.
The vocalizations accompanying food begging display in young birds are structurally quite different from the begging "keu" that accompanies courtship feeding solicitation d isp lay of a d u lts . However, to the human observer, the two calls sound alike. Their differences will be discussed later in the chapter on acoustic signals.
Precopulatory display and copulatory position (Fig.
18). This display, given only by adult females ready for copulation, is like courtship feeding solicitation, but its features are more exaggerated. Specifically, the wings and
tail are fully open and very vigorously fluttered. At the
same time, the body is completely, rather than partially,
crouched during the display. Precopulatory display, like
courtship feeding solicitation display, is invariably Figure l8. Precopulatory display and copulatory position. 63
r \ 64 accompanied by the begging "ken" call. Unfortunately, I have not observed copulation or recorded it on film. Its description awaits further observation. CHAPTER IV
VOCALIZATIONS
Introduction
Many Blue Jay vocalizations have been previously described by Amadon (19^^)? Bent (1546), Hardy (1961, 196*+,
1969), and Edwards (1971)* Some of these descriptions have included sonagraphic analyses (Hardy, 196*+, 1969; Edwards,
1971); however, detailed descriptions of most of the parameters of vocalizations have not been published.
Similarly, although some authors have suggested functions of some of the v o c a liz a tio n s (Amadon, 19*+*+; Hardy, 196I;
Edwards, 1971), no study directed primarily at determining the function of Blue Jay vocalizations has been published.
Vocalization Parameters In discussing the results of sound analyses, 1 w ill describe the following parameters of each vocalization: number of sound sources, fundamental frequency, number and frequency of harmonics, dominant frequencies (in vocalizations with harmonics or with elements produced by both sound sources), inflection, frequency modulation, and 65 66 temporal characteristics (including the number and duration of notes or clicks). Amplitude modulation is present to some degree in almost all vocalizations, and it will not be d iscu ssed . A few terms should be defined to avoid confusion. In addition, because many terms, as well as names of vocalizations, will be used quite frequently, I will give an abbreviation or symbol for the terms the first time they are introduced, and, thereafter, use the abbreviation. The Appendix lists all the terms and their symbols in alphabetical order.
The frequency of a sound is the number of full sound waves (cycles) per second. The unit in which frequency is expressed is Hz (hertz) or KHz (kilohertz). One Hz is equal to one cycle per second, while one KHz is equal to 1,000 cycles per second. Because the narrow band pass filter of
the Sonagraph has a frequency resolution of only *+5 Hz, and because there are many abrupt, extensive, and irregular
changes in frequency within individual calls, I have reported
only ranges, rather than averages, of frequencies for the different groups of calls.
A harmonic is a sound caused by non-sinusoidal
vibration of the sound source (88), and whose frequency is
some integer multiple of a fundamental frequency (F). Frequency and amplitude modulation (FM and AM, respectively)
are changes, not necessarily regular, in the frequency and 67 amplitude of the sound. In this paper I will describe large, long, irregular changes in frequency as changes in inflection, and small, short, fairly regular changes as FM. Birds that have a tracheo-bronchial syrinx, and this includes the Blue Jay, are capable of producing two different sounds simultaneously (Miskimen, 1951)* When a vocalization is made up of two different sounds, they may be identified if they are of different F or, when they are of the same F, if each sound is amplitude and/or frequency modulated in a different manner.
Vocalizations
I have made tape recordings of all of the vocalizations given by my hand-raised Blue Jays and performed sonagraphic and oscilloscopic analyses of as many recordings as possible of each type of vocalization. In addition, I have attempted to determine the function of each vocalization by observation and, in some cases, by experimentation. The function of a particular call is influenced by 1) the physical characteristics of the call, 2) postures associated with the
call, and 3) the behavioral context of the call.
Some of the vocalizations I have analyzed are similar
in structure as well as function. These similarities prompted me to group the calls into four categories: 1) harmonic spectra, 2) pumphandle calls, 3) click calls, and 4) song.
The calls in the harmonic spectra group are 68 physically similar in that they are rich in harmonics. The physical attributes by which they differ are the number of
88, the F, inflection and the nature of modulations.
Functionally these calls are indicators of alarm, frustration, and excitement associated with fear. They may also serve as
contact notes within a flock, among family members, or
between members of a pair. The pumphandle calls have two 88, similar AM and FM, and a lack of pronounced inflection. They differ in F and the number of harmonics present. Functions of these calls
include the indication of mild excitement and uncertainty,
and they also may serve as territorial or alert calls.
The click calls are characterized by the presence of
harmonics, presence of clicks, strong and regular AM and FM and terminal downward inflection. They may be distinguished
from each other by their F and the number of 88 present.
They function to indicate excitement associated with both
frustration and fear.
The physical characteristics of song are highly
variable. However, it is a distinctive vocalization type in
that its phrases, as well as entire singing bouts, are quite long, occasionally lasting over two minutes. 8ong is the sole vocalization given by the male during courtship. It is also given intermittently by birds in a calm behavioral state.
All of the illustrations of vocalizations in this paper consist of two types of sonagrams. The sonagrams on 69 the left in each illustration were made with the narrow hand pass filter, which has a frequency resolution of ^5 Hz. Those on the right were made with the wide band pass filter, which has a frequency resolution of 300 Hz and a temporal resolution of 1.5 ms (milliseconds). Sonagrams made with the narrow band pass filter have poor temporal resolution. All sonagrams were made at the frequency band setting that has
lower and upper effective resolutions of 80 and 8000 Hz,
respectively.
Harmonic Spectra
The D istre ss C all (DC, F ig. 19) is given by b ird s
that are being handled, confined (such as in a very small
cage, an insect net, or a mist net), or chased. The only
body posture consistently associated with this call is
crouching in its most extreme form.
The DC has the form of a simple cry; that is, it has
a rainbow-shaped sonagram (Davis, 19640, indicating that the
frequency builds and then drops as the mandibles open and
close. The call contains elements from both 88. The first
and most obvious sound (81) is responsible for the shape of the sonagram. The F of 81 starts between C.5C and 1.6C KHz,
r is e s a maximum of C.3C KHz or a minimum of C.2C KHz, and,
from this point, drops C.3C to C.4C KHz. 81 may have from
4 to 11 harmonics, among which dominance shifts from higher harmonics at the onset of the call to lower harmonics
as the frequency rises and then back to higher harmonics as F igu re 19. The Distress Call (DC) 8 KHz r
7 KHz
6 KHz
5 KHz
4 KHz
3 KHz
2 KHz
0.5 sec. 1.0 sec. 1.5 see. 72 the frequency drops. The most Intense harmonics are the first through the fourth The duration of SI ranges from 225 to 600 ms (avg. = ^12). The second sound (82) begins 25 to 50 ms after the first, at a frequency between O. 7O and 1.00 KHz. It is slightly downwardly inflected (about 0.10 or 0.20 KHz) until the end of the call. This sound is usually frequency modulated during the last 100-150 ms of the call. The modulation is of about O .50 KHz, but varies. 82 may have 6 to 11 harmonics, the most im portant ones being Hl-H^-. The duration of 82 ranges from 200 to 350 ms (avg. = 275)* The Alarm Call (AC, Fig. 20). A Blue Jay that spots a potential predator usually gives this vocalization. In 7^ cases where such a potential predator was within sight of my captive birds, this call was given 63 times (85^)* Calculation of the Chi-square statistic to test whether the behavior is associated with the call more than 50^ of the time showed that there was an association between the two (X2 = 36. 5^, P< .005)' Of 213 observations when the posture associated with the call was noted, 85 calls (40%) were given with simple bobbing (usually the exaggerated type), 68 ( 32 ^) with the mild or intense aggression posture and 60 ( 28^) w ith the neutral posture.
The AC has only one 88 and has from five to seven harmonics, the most intense of which are HI-H^. The F of
these calls is never as intense as any of the harmonics. F ig u re 20. The Alarm C all (AC) 8 KHz r
7 KHz
6 KHz
5KHz
4 KHz
3 KHz
2 KHz
I KHz
0 0.5 sec. 1.0 sec. 75 During the first 25 ms of the AC there is a sharp rise in frequency of 0.05 to 0.20 KHz. In the next 50 to 100 ms the frequency remains stable and then, in the next 100 to
150 ms either remains stable or drops about 0.05 KHz. The frequency continues to drop 0.05 to 0.10 KHz during the rem ainder (125 to 3 OO ms) of the c a l l . The call usually contains FM at two different points—from 75 to 150 ms and from 75 to 125 ms during the last half of the call. The duration of AC calls ranged from
300 to 4/5 ms with an avg. of 389 ms. The Flock Contact C all (FC, F ig . 21). During the non-breeding season (August through February), Blue Jays often travel in flocks (Hardy, 196I; Sutton, 1966). When members of the flock are scattered or when they are not in sight of each other, they give the FC. By observing the context in which the FC was given, as well as by determining how often
the call is given when birds were or were not in flocks, I hypothesized that the FC was used as a contact note; that is,
the FC is given by birds as a means of acoustically specifying
their location to other birds in the flock, who, in turn, are able to "keep track" of their flock mates acoustically.
Although the FC is heard throughout the year, it is
more frequent during the non-breeding season. In 1969 and
1970, at least once a week, I recorded the number of FC given
by both captive and wild birds for an hour. Observations
were made between 0900 and 1100. Fig. 22 is a graph of the number of FC per hour during each month of the year. Figure 21. The Flock Contact Call (FC). 8 KHz
7 KHz
6 KHz
5 KHz
4 KHz
3 KHz
2 KHz
0.5 sec. 1.0 sec. 1.5 sec. Figure 22. The number of Flock Contact Calls per hour throughout the year. £r =) o X 30 cr LÜ Q_ 25 -
œ
20 - 6
I 5 ; 8 10 - o Q
0. asondjf mA M J J non-breeding season MONTH breeding season 80 The number of FC per hour during the non-breeding season is higher (avg. = 29) than that during the breeding season (avg. = 15)* When the weekly means of FC per hour in the two seasons are compared, there is a significant difference (t = 9*36, .005) between the two groups. The FC is associated with simple bobbing, neutral or maintenance postures. The FC has two 88, the first being of a relatively low F (0.40 to 0.90 KHz) with five to seven harmonics. H3 is always the dominant frequency, with HI, H2, and H7 also being quite intense. The F is rarely more intense than any of the harmonics.
Regardless of the value of the F at the onset of the call, it is warbled over a range of 0.50 to 1.50 KHz above and below the initial value throughout the duration of the FC.
The duration of 81 ranges from 375 to 475 ms (avg. = 432).
The value of the F of 82 in the FC ranges from 0.90 to 1.80 KHz. There are always two harmonics, either one of which may be dominant. The F is always less intense than either harmonic. 82 begins from 25 to 200 ms after 81 and
is warbled throughout its duration from 0.25 to 1.20 KHz above and below the F. There is usually a terminal downward
inflection. The duration of 82 is from 150 to 400 ms (avg. =
373). The FC of young (one to three months of age) Blue
Jays (YFC, Fig. 23) differs in some notable ways from that of
adults. The F of 81 is generally higher in value (0.75 to Figure 23. The Flock Contact Call of young Blue Jays (YFC). 8 KHz
7 KHz
6 KHz
5KHz
4 KHz
3 KHz
2 KHz
I KHz
0 0.5 sec. 1.0 sec. 83 1.65 KHz) and has fewer (none to four) harmonics. The duration of this sound has a greater range (350 to 500 ms) and it is, o% the average, longer (avg. = ^ 37)* 82 in the YFC has an F higher than that of the 82 F in the adult call (1.85 to 2.40 KHz). It usually has the same number of harmonics, but the F may be more intense than e ith e r (but not both in the same c a ll) harmonic. The duration of 82 ranges from 300 to 525 ms and it is longer
(avg. = ^-*+3 ) than that of 82 in the adult call. The Young Food-begging Calls (YFB, Figs. 24-2?) are quite variable and I have divided them into four types:
YFB1, YFB2, YFB3, and YFB^-. All YFB calls are given by nestling or fledgling birds as they beg for food. These calls are accompanied by the young food-begging posture (see Chapter III) about 50^
(32 of 65 cases) of the time in two- to three-week-old nestlings and about 80^ (27 of 3^ cases) of the time in fledglings. YFB1 and YFB2 are given by birds that are at least about l4- days old. YFB3 calls are given by one- to
three-week-old nestlings and rarely by fledglings, while YFB>+
calls are given by nestlings less than about 10 days old.
YFB1 calls (Fig. 2^) have only one 88, whose F ranges from 0.70 to 1.20 KHz, and they have five to nine harmonics.
The order of dominance of harmonics is sequential, HI always being the dominant, H2 second in intensity, and so on. The F is always the least intense frequency. F ig u re 2h. The Food-begglng Call of young Blue Jays, Type 1 (YFB1). 8 KHz r-
7 KHz
6 KHz
5KHz
4 KHz
3 KHz
2 KHz
I KHz
0.5 sec. 1.0 sec. Figure 25. The Food-begging Call of young Blue Jays, Type 2 (YFB2). 8 KHz
7 KHz
6 KHz
5 KHz
4 KHz
3 KHz
2 KHz
I KHz
0.5 sec. 1.0 sec. 88 There is a decrease in frequency throughout most calls that is abrupt during the first 0 to 50 ms and then slower for the rest of the call. Total decrease in frequency ranges from 0.05 to 0.50 KHz, but is usually less than 0.10
KHz. YFB1 calls are relatively short in duration, lasting from 100 to 300 ms (avg. = 209). YFB2 calls (Fig. 25) may have one or two 88, the
first of which has an F of from O.3 O to 2.00 KHz, but usually
between 0.60 and O. 9O KHz. The sound is often w arbled from
0.50 to 1.50 KHz above and below the F, but the F may be
constant throughout the call. There are from one to ten
harmonics (usually five to eight), and HI is dominant, H2-H4-
also being quite intense. The F is never more intense than
any of the harmonics.
The duration of the first sound is from 75 to 1000 ms
(avg. = 395). 82, which appears in 5 out of 16 calls, begins 100 to
4-50 ms after 81. It has an F of 0.50 to 3*30 KHz, and remains
constant in three out of five cases. When it does not remain
constant, it is warbled from 0.25 to O. 3O KHz above and below
the F. There are no harmonics. 82 has a duration of 100 to
350 ms (avg. = 225).
YFB3 calls (Fig. 26) are short notes given in series.
Of 21 YFB3 analyzed l4- had two 88. 81 has a F of 0,90 to
2.80 KHz. During the first 25 ms of most calls the frequency Figure 26. The Food-begglng Call of young Blue Jays, Type 3 (YFB3). W
0.5 sec 1.0 sec. 1.5 sec. 91 is inflected upward 0.10 to 0.80 KHz and then drops back down
0.20 to 0.40 KHz. Occasionally, the F may simply drop 0.10 to O.hO KHz. The F may simply drop 0.10 to O.^fO KHz in the first 25 ms. For the next 50 ms the F remains the same or is in fle c te d downward 0.10 to O. 3O KHz. If the note is longer than 50 ms there may be another warble of the F through about
0.10 or 0.20 KHz or it may remain the same. SI of YFB3 calls is quite short in duration, ranging from 25 to 150 ms (avg. =
69). 82 of YFB3 calls have a F of from 2 .7O to 3-90 KHz.
In the first 25 ms the F drops 0.10 to 0.20 KHz or is sharply inflected upward 0.10 to O. 7O KHz and then drops 0.10 to 0.20
KHz. In the next 25 ms the frequency continues to drop another 0.10 to 0.20 KHz, and, thereafter, remains the same if the call is longer than 50 ms. 82 is short, except in a few cases, lasting from 50 to 150 ms (avg. = 77)*
Both 81 and 82 characteristically have one harmonic, although in 6 of 38 cases there are no harmonics and in 3 of
38 calls 81 had five harmonics. The F is the dominant frequency except in the three calls which had five harmonics.
In those cases the order of dominance of harmonics is
sequential, HI being the most intense and the F least intense,
YFB>+ (Fig. 27) vocalizations have two 88, neither of which has harmonics, and both of which have strong FM.
81 in the two calls examined started at 3.4-0 and 4.00
KHz and was warbled throughout the call over a range of O. 3O Figure 27. The Food-begging Call of young Blue Jays, Type h (YFB^-). 8 KHz
7 KHz
6 KHz
5 KHz
4 KHz
3 KHz
2 KHz
I KHz
0.5 sec. 1.0 sec. 1.5 sec. 9^ to 0.50 KHz. The d u ra tio n of 81 in one c a ll was 100 ms, in the other, 7OO ms. 82 in the first call started at 3 .10 KHz, in the second a t 2 .7O. Both sounds were warbled continuously from
0.20 to 0.^-0 KHz. The d u ra tio n of 82 in one case was 600 ms and in the other 7OO ms. The Begging Keu Call (BK, Fig. 28) is the vocalization that characteristically accompanies courtship feeding and probably copulation. Although I have not observed copulation, in 209 of the 256 cases (82#) when 1 recorded the vocalization accompanying courtship feeding, it was BK. The remaining cases were either unaccompanied by vocalization or were accompanied by the 8K. Calculation of Chi-square shows BK to be associated with courtship feeding more than 50# of the
time (X2 = IO5.O8, P< .005).
Three BK were analyzed, and their F values were I. 70,
1.70 and 1.80 KHz. In the f i r s t 100 ms each c a ll was
inflected downward 0.10 KHz and then remained at that
frequency for the rest of the call. All of the F were warbled
or frequency modulated about 0.60 KHz above and below the F
throughout their duration. There were two harmonics in each
call; HI was the dominant frequency and H2 the least intense
frequency. The three calls lasted 125, 150 and 200 ms (avg. =
158). The 80ft Keu Call (SK, Fig. 29) functions as a
contact note between members of a pair or among members of a Figure 28. The Begging Keu Call (BK) 8KHz r
7 KHz
6 KHz
5 KHz
4 KHz
3 KHz
2 KHz
I KHz
0.5 sec. Figure 29. The Soft Keu Call (SK) 8KHz I-
7 KHz
6 KHz
5 KHz
4 KHz
3 KHz
2 KHz
I KHz
I_____ 0 0.5 sec. 1.0 sec. 99 family group when birds are relatively close to each other.
I tested the hypothesis that the SK functioned in this manner by recording the number of tim es the SK was given by members of a pair or family of captive or wild birds when they were less than 10 m apart and when they were more than 10 m apart.
Of a total of 731 SK recorded, 627 (85^) were given by birds less than 10 m apart. This is significantly more (X^ = 37^.18, P< .005) than the number of SK (10^ or lh^) given by birds more than 10 m apart. Birds giving the SK are usually in neutral or maintenance posture. Occasionally, they are
involved in courtship feeding. The SK is a very simple call with no inflection of the F, constant FM, a rich harmonic
spectrum and a short duration. F ranges from 0.60 to 2.00
KHz and is modulated 0.10 to O. 3 O KHz throughout its duration.
There are from two to five harmonics with the dominant
frequencies being HI or F. Other harmonics of high intensity are H2 and H3. The SK varies in length from 25 to 300 ms
(avg. = 193)' The Loud Keu C all (LK, F ig. 30 ) may connote frustration
(as when a bird can see, but cannot get to a food dish or its
mate) or hunger (in adult birds). In these cases, especially
the latter, the call is occasionally accompanied by fluttering of slightly fanned wings. Simple bobbing was recorded in 1 7
of 113 cases (15^) when the posture associated with the LK
was noted. The LK serves most often as a contact note
between members of a pair that are more than about 10 m apart. P ig ure 30* The Loud Keu C a ll (LK). 8 KHz
7 KHz
6 KHz
5 KHz
4 KHz
3 KHz
2 KHz V :
I KHz
O 0.5 sec. 1.0 sec. 1.5 sec. 102
Of 324 LK, 267 (73#) were given by birds more than 10 m away from their mates. The Chi-square test shows this to be significantly (X^ = 136.II, P< .005) higher than the number of LK given by birds less than 10 m from their mates. The F of LK varies from 1.20 to 1.50 KHz. During the first 100 ms the call is inflected either up or down 0.10 KHz or remains at the same value. Regardless of whether the call is inflected up or down at its onset, after the first 100 ms the frequency drops continuously 0.10 to 0.40 KHz for the rest of the call. There are from two to five harmonics in LK. The
order of dominance of harmonics is usually sequential except
that F is usually between HI and H2 in intensity.
The duration of LK ranges from 400 to 650 ms (avg. =
486).
The Crow Call (CC, Fig. 31) is one of many examples
of mimicry in the vocal repertoire of my captive Blue Jays.
The jays learned this call from Common Crows (Corvus
brachyrhyncos) which fed near their outdoor flight. The call is given intermittently and I have not been able to determine
i t s fu n ctio n , i f , indeed, one e x is ts . The CC has the form of a simple cry and the F ranges
from 0.50 to 0.70 KHz. During the first 50 ms the F
increases by 0.10 KHz, and, in the second 50 ms it drops
back to the original value. Thereafter, the F either remains
co n stan t or is d e fle c te d downward another 0.10 KHz. F ig u re 31. The Crow C a ll (CC). 8KHz r
7 KHz
6 KHz
5 KHz
4 KHz
3 KHz
2 KHz
0.5 sec. 105 The CC is rich in harmonics, each call having from 6 to 11. Dominant frequencies are HI and F. Other frequencies of high intensity are H2-H5* The duration of all the CC analyzed is 150 ms. The mimicked calls compare quite well with published sonagrams
(Chamberlain and Cornwell, 1971), with respect to physical characteristics. The Meow Call (MC, Fig. 32) is another example of vocal mimicry that has no apparent function. During the time I kept them at my home, the captive jays learned to imitate the meow of a pet Siamese cat (sonagram, Fig. 33)»
The cat's MC has an F of O.H-0 KHz that remains constant throughout the 1200 ms call. There are five harmonics, H3, F, and HI being most intense in that order.
The Blue Jay MC calls have F of from O.H-O to O.yO KHz and take the form of a simple cry. ■ During the first 300 to
*+00 ms, the F is inflected upward 0.10 KHz and then drops back to the original value during the rest of the call.
There are from three to seven harmonics and the dominant frequencies are the same as for the cat's MC.
The duration of Blue Jay MC calls ranges from 700 to
1100 ms (avg. = 87I).
With the exception of changes in inflection, the Blue
Jay MC calls are very similar to the cat MC calls in structure.
Table 2 is a summary of the physical characteristics of the calls in the harmonic spectra group, and Table 3 lists the
functions and postures associated with these vocalizations. F ig ure 32 . The Meow C a ll (MC). 8 KHz
7 KHz
6 KHz
5 KHz
4 KHz
3 KHz ; I.;: 2 KHz II I KHz -
0.5 sec. 1.0 sec. 1.5 sec. F igu re 33 . The meow of a cat. 4 KHz
3 KHz
2 KHz
KHz
0.5 sec. 1.0 sec.
4 KHz r
3 KHz
2 KHz
1 KHz
0.5 sec. 1.0 sec. Table 2 .—Physical characteristics of the harmonic spectra calls
F D uration (ms ) No. of Dominant No. of C all 88 (KHz) Mean SE CV Harmonics Frequency FM I n f le c tio n C a lls
DC 1 0 . 50- 1.60 412 153 64 4 -1 1 v a rie s up th en 3 down
DC 2 0 . 70- 1.00 275 61 38 0 F X down 3 AC 1 0 . 55- 0.65 389 22 15 5-7 HI -h4 X up th en 7 down
FC 1 0 .40 - 0.90 431 9 7 5-7 H3,H1,H2 X none 15
FC 2 0 . 90- 1.80 373 18 28 2 HI or H2 X down 15 (te rm in a l)
YFC 1 0 . 75- 1.65 438 13 13 0-4 H3,H1 X none 18 YFC 2 1 .8 5 -2 .4 0 443 l4 14 2 HI,H2, X down 18 or F (te rm in a l)
YFB1 1 0 . 70- 1.20 209 20 38 509 H1,H2,H3 down l4 YFB2 1 0 . 30 - 2.00 39$ 54 51 1 -10 H1,H2,H4 X none 16 YFB2 2 0 . 70- 3.30 265 45 44- 0 F X none 5 Table 2. Continued
F D uratio n (ms) No. of Dominant No. of C all 88 (KHz) Mean SE CV Harmonics Frequency FM I n f le c tio n C a lls
YFB3 1 0 . 90- 2.80 69 8 58 0 H1,H2,H3, X up then 20 e tc . down or down
YFB3 2 2 . 70- 3.90 78 10 51 0 HI X up then 14 down or down
YFB^- 1 3 .4 0 -4 .0 0 ^38 175 47 0 F X v a rie s 2
YFB1+ 2 2 . 70- 3.10 650 50 11 0 F X v a rie s 2
BK 1 1. 60- 1.80 158 22 24 2 HI ,F,H2 X down 3
SK 1 0 .6 0 -2 .0 0 193 10 47 2 -5 H I, or F X none 80 LK 1 1.20- 1.50 486 36 19 2-5 HI,F,H2 up then 7 down or down CC 1 0 . 50- 0.70 150 0 0 6-11 HI,F,H2 up th en down 10 MC 1 0 .40 - 0.70 871 61 18 3-7 H3,F,H1 up th en down 7 112 Table 3*—Postures and functions associated with calls in the harmonic spectra group
Vocalization Postures Functions
DC crouching, flight, distress, fright
being handled
AC simple bobbing, mild alarm
or intense aggression, n e u tra l
FC and YFC neutral, simple flock contact
bobbing, maintenance
YFB1- crouching, wing and food solicitation YFB^- tail fluttering
BK crouching, wing and courtship feeding
tail fluttering solicitation
SK neutral, maintenance. pair or family
courtship feeding contact (proximal) LK simple bobbing, wing pair or family
and tail fluttering contact (distance),
frustration, hunger
CC v a rie s ?
MC v a rie s 9 113 Pmnphandle Calls
The B ell Song (BS, Fig. 3^-) is th e p rin c ip a l territorial call of the Blue Jay. It also may be given in situations where the bird is excited by a strange object, noise, or animal in or near the cage. In such instances the BS may be given as an "alert signal" by one bird, apparently serving to call attention to something or, on the other hand, it may simply be an expression of the excitement generated by a strange circumstance.
The BS is accompanied by simple bobbing in 28 of 71 cases (*+0^) for which calls and postures were recorded simultaneously. Calls accompanied by simple bobbing were given in the territorial context. Other postures accompanying this call are the neutral and investigatory postures. The latter posture usually accompanies the BS of a highly excited b ird .
BS calls usually have two clear notes, each of which is produced by a different SS. SI has an F of 2.30 to 2.90
KHz which is rarely inflected up or down. If there is
inflection it never exceeds 0.10 KHz. 81 occasionally has one, rarely two, very low intensity harmonics. The F is
often modulated about 0.50 KHz above and below the F. The duration of S1 ranges from 250 to 350 ms (avg. = 267).
82 of the BS begins 175 to 225 ms after SI at an F of 1.50 to 1.70 KHz and remains at the in itial value throughout
its duration. There are no harmonics and the duration of 82 ranges from 50 to 200 ms (avg. = 113). F ig u re 3^* The B e ll Song (BS) 8 KHz
7 KHz
6 KHz
5KHz I 4 KHz I
3 KHz
2 KHz
I KHz
0 0.5 sec. 1.0 sec. 116 The first attempts of BS of one- to three-month-old
Blue Jays differ from adult BS calls in a number of ways.
The YBS (Fig. 35) calls have two 88. In general F of YB8 81 is lower than those of B8 81 (1.80 to 2.80 KHz). The F of 81 is usually inflected up from 0.10 to 1.00 KHz and then down 0.10 to 1.80 KHz, but may remain stable. The F is often modulated to the same degree as 81 of B8. Sometimes there
are three or four harmonics, but the F is the dominant
frequency. YB8 81 are longer than B8 81, ranging from 275 to
600 ms (avg. = 427). 82 of YB8 may begin before, after or simultaneously
with 81, and the F ranges from 1.00 to 2.90 KHz. 82 often
has up to three harmonics with the F being dominant.
Modulation of YB8 82 is similar to that of B8 82. The 82 is quite long, lasting from 125 to 550 ms (avg.= 4o6). The Wheedle B ell Song (WB8, Fig. 36) sounds s im ila r to
the B8, but is quite different in structure. It is given by
mildly excited birds and also by birds which appear to be in
situations which involve uncertainty, possibly because of a
conflict of drives exists. For example, a captive jay may be
quite hungry but reluctant to approach a feeding station,
perhaps because there is a strange human (a person other than the author) in the cage. The WBS is often given by a bird in
such circumstances. In situations of uncertainty the WB8 is
usually unaccompanied by neutral or investigatory postures,
whereas when the WB8 is an apparent expression of excitement Figure 35. The Bell Song of young Blue Jays (YBS). 8 KHz
7 KHz
6 KHz
5 KHz
4 KHz
3 KHz
2 KHz
I KHz
0 0.5 sec. 10 sec. F ig u re 36. The Wheedle B e ll Song (WBS). 8 KHz
7 KHz
6 KHz
5 KHz
4 KHz
3 KHz
2 KHz
I KHz
0 m - * e — 0.5 sec. 1.0 sec. 1.5 sec. 121
(1^ of the 56 call and posture recordings [ 25^]), it is accompanied by simple bobbing. The f i r s t of the two 88 of the WB8 has an F of from
3.30 to 3*80 KHz. During the first 100-150 ms, the F may rise 0.10 KHz and thereafter decrease 0.10 to O. 7O KHz. 8ometimes the F simply decreases from beginning to end of the
call. In most cases 81 is strongly but irregularly frequency modulated. If 81 was harmonics, there is only one and it is
less intense than F. The duration range of 81 is 300-^+50 ms
(avg. = 3 ^ 1). 82 of the WB8 begins 100-200 ms after 81 at an F of
2.10 to 3-00 KHz and remains at the initial value until it
stops. There are no harmonics, but, as in 81, there is usually substantial but irregular FM. The duration range of
82 is 100 to 300 ms (avg. = 225).
Table ^ lists the physical characteristics and Table 5
lists the functions and postures associated with the pumphandle calls.
Click Calls
The Rolling Click Call (RC, Fig. 37) is always
accompanied by simple bobbing (one or two bobs per RC), and, apparently, is exclusively a female vocalization. I have
sexed my captive animals behaviorally during the breeding
season. The animals observed to give the RC were either
unsexed, because they did not mate, or were classed
behaviorally as females. The RC indicates excitement Table h .—Physical characteristics of the prunphandle calls
F D u ratio n (ms) No. of Dominant No. of C all SS (KHz) Mean SE CV Harmonics Frequency FM I n f le c tio n C alls
BS 1 2 . 30 - 2.90 267 7 22 0 F X none, up 9 or down
BS 2 1 . 50-1 .70 113 17 46 0 F X none 9
YBS 1 1. 80- 2.80 427 26 34 0-4 F X up th en 13 down
ro YBS, 2 1.00- 2.90 406 35 38 0-3 F X none 13 WBS 1 3 . 30 - 3.80 341 21 17 0-1 F X down or up 8 th en down
WBS 2 2 . 10- 3.00 225 2 6 33 0 F X none 8 123 Table 5*—Postures and functions associated with the pumphandle c a lls
Vocalization Postures Functions
BS and YBS simple bobbing, territorial, alert. n e u tr a l, excitem ent investigatory
WBS simple bobbing, mild excitement.
n e u tra l. uncertainty investigatory F ig u re 37. The Rolling Click Call (RC). 8 KHz I-
7 KHz
6 KHz
5 KHz
4 KHz
3 KHz
2 KHz
I KHz
0 0.5 sec. 1.0 sec. 126 associated with fear. Specifically, it seems to be associated with a thwarted drive to flee. For example, some of the captive female jays were not very tame and
■usually avoided me. However, when they were confined in small enclosures for special observation, they were unable to m aintain much d istan ce between me and them selves. I t was in these circumstances that the RC was most often observed.
Occasionally, the RC seemed to function as an alert signal in the same fash io n as the BS.
The RC is made up of two series of clicks with voiced sound (only one series is shown in Fig. 37)* The first series of clicks contains 15 to 17 clicks (avg. = 16.6), 23 ms a p a rt and the second series contains 1*+-16 (avg. = 15*8) clicks 23 ms a p a rt. The se rie s them selves are from 60 to 210 ms a p art
(avg. = 87. 8), but only one in te r v a l was more than 80 ms
long. If this aberrant interval is omitted, the avg. is
72.5 ms. The voiced sound has only one SS whose F is from I .70
to 1.90 KHz in the first click series and from 1.80 to 2.00
KHz in the second series. The F is inflected down 0.10 to 0.20 KHz over the duration of each series of clicks. This is probably due to the closing of the mouth, which is easily
observed. A further indication that the mouth is closed as
the call progresses is the shift in intensity of harmonics.
The first four clicks always have two harmonics, but, as the
F decreases, only one or no harmonic is present. 127 The Descending Whistle (DW, Fig. 38) indicates excitement and, like the RC and BS calls, may serve as an alert note. It is accompanied by simple bobbing 20^ of the time it is given and also by neutral and investigatory p o stu re s. The DW contains clicks with voiced sound from two SS.
During the first 10*+ to 115 ms (D¥1 in Table 6) the F of SI s t a r ts a t 2.^-0 to 2 .7O KHz and drops O. 7O to 1.20 KHz. This part of the call has I7 or 18 clicks, each 27 or 28 ms apart. There is one harmonic, which is much more intense than the F.
During the next 50 to 60 ms (DW2 in Table 6) (avg. = 56) of
the call there are no clicks and the F drops rapidly 1.1+0 to 2.60 KHz.
S2 usually begins about 25 to 28 ms after SI and has
three to nine clicks (avg. = 6.6) 25 to 35 (avg. = 28) ms
a p a rt. The F is 3*30 to 4.00 KHz and u su a lly drops 0.10 to
0.60 KHz and then rises 0.20 to 0.60 KHz. There are no
harm onics. The average d u ratio n of S2 is 56 ms.
The Growl (GR, F ig. 39), to which I have n o t been
able to assign a function, is accompanied by neutral or
maintenance postures. There are one or two SS, the first of which has an F of O.7O to I .80 KHz. The F is inflected up
sharply O.50 to 3*40 KHz during the first 150 to 250 ms of
the call. During the next part of the call the F remains
fairly stable and then drops rapidly 0.60 to 3 .30 KHz over a
period of 50 to 150 ms. There are 5 to 14 clicks (avg. =
7.9) in SI from 20 to 50 ms (avg. = 25) apart. Harmonics are F ig ure 38. The Descending Whistle (DW) 8 KHz
7 KHz
6 KHz
5 KHz
4 KHz
3 KHz
2 KHz
0.5 sec. 1.0 sec. 1.5 sec. F ig u re 39. The Growl (GR) 8 KHz
7 KHz
6 KHz
5KHz
4 KHz
3 KHz
2 KHz
I KHz
0 0.5 sec. 1.0 sec. 132 not present. The duration of 81 ranges from 125 to 4-50 ms
(avg. = 230 ). 82, when it is present, has an F of 0.60 to 1 .80 KHz, which remains stable with respect to overall inflection, but which is frequency modulated through about 0.4-0 KHz. There
are from 9 to 13 clicks (avg. = 11.0) 20 to 4-0 ms (avg. =
29) apart. The duration of 82 ranges from 75 to 575 ms
(avg. = 300 ). The Triple Descending Whistle (TDW, Fig. 40)
functions as a territorial call, an alert call or as an "announcement of victory" occasionally given by the winner
of an aggressive encounter. When the TDW serves as an alert
call it is accompanied by neutral posture or, infrequently,
simple bobbing, whereas, when it is a territorial call or
victory announcement, it is usually accompanied by simple
bobbing or neutral posture. The TDW is actually a series of three short whistles
originating from only one 88. Clicks are irregularly present
in most TDW. The TDW usually has four distinct notes. The
first note, when present (4-2^ of TDW analyzed), is 10 to 20
ms long (avg. = I 8) and its F is from 1.00 to 1.60 KHz. It
has no harmonics. The second note, 15 to 28 ms (avg. = 22),
has an F of 1.50 to 2.10 KHz. It is present in all TDW
analyzed and has no harmonics. The third note is rather long,
lasting 75 to 95 ms (avg. = 82) with an F of I .90 to 2.90 KHz, which remains constant except in a few cases, when it is Figure 1+0. The Triple Descending Whistle (TDW). 8 KHz
7 KHz
6 KHz
5 KHz
4 KHz
3 KHz
2 KHz
0.5 sac 1.0 sec. 1.5 sec. 135 inflected upward 0.10 to 0.20 KHz. This note usually has two harmonics and the order of dominance of the frequencies is F, HI, H2. The last note is also long, ranging in duration from
55 to 90 ms (avg. = 69), and the F, which begins at 2.50 to 3.20 KHz, drops sharply I .30 to 2 .7O KHz. The harmonic spectra and dominant frequencies are the same as in the third n o te.
Tables 6 and 7 list physical and behavioral parameters of the click calls.
Song
Song in the Blue Jay is given by both sexes and usually consists of a long series of phrases, the characteristics of which include all of those present in the other three call groups. Most of the vocalizations in those groups are included verbatum in song, along with many series of short whistled notes. Blue Jay songs are very long in duration, frequently lasting over two minutes. Because songs are so long and because they are, essentially, a conglomeration of all the previously described vocalizations,
I have not included a sonagram of this vocalization.
Song in the Blue Jay, as I have called it, is a type
of primary song (Berger, 1961). Specifically, it is a signal
song, that is, one that is used to coordinate the activities
of a pair. It is given by the male during courtship bobbing,
but never functions as an advertising or territorial song.
Song is also given when a bird is relaxed, perching, or 136 Table 6. —Physical characteristics of the click calls
F D uration (ms) No. of Call SS (KHz) Mean SE CV Harmonics
RCia 1 1. 70- 1.90 358 11 7 0-2 RC2& 1 1. 80- 2.00 335 9 6 0-2 DW1^ 1 2 .40 - 2.70 27 1 5 1 DWib 3 . 30 -4.00 56 1 8 0 DW2^ 1 1.20-2.00 28 2 4 0
GR 1 0 . 70- 1.80 230 35 44 0
GR 0 .60- 1.80 300 85 0 TDW1° 1 1 .00-1.60 18 1 21 0
TDW2C 1 1 . 50- 2.10 22 1 17 0
TDW3 C 1 1 .90- 2.90 82 1 7 0-2
TDW^c 1 2 . 50- 3.20 69 2 15 0-2
%C1 and RC2 represent the first and second series of clicks in each call.
DW1 and DW2 represent the first and second parts of the DW.
"TDW1 - TDW4- represent the 4- notes of TDW calls as discussed in the text. 137 Table 6. Continued
In te rv a l Dominant No. of between Nd . of Frequency FM Inflection c lic k s c lic k s (ms) c a lls
F down 15-17 23 7
F down 1'+-16 23 7
H1 • down 17-18 27 6 F down 3-9 28 6 F down 0 0 6
F up then down 5-1^ 26 10
F none 9-13 29 10 F none v a ria b le v a ria b le 10 F none or up variable variable 21
F,H1,H2 none or up v a ria b le v a ria b le 27 F,H1,H2 down variable variable 25 138 Table 7.—Postures and functions associated with the click c a lls
Vocalization Postures Functions
RC simple bobbing by alert, excitement female (fear) thwarted drive
to f le e
DW simple bobbing, alert, excitement
investigatory, n e u tra l
GR neutral, maintenance ?
TDW simple bobbing. territorial, alert
n e u tra l victory announcement 139 moving about. In these cases it has no apparent function other than that it is an indication that the bird is in a calm behavioral state. CHAPTER I I I
DISCUSSION AND CONCLUSIONS
Origin and Significance of Postures and Displays
The functions of visual communication signals of Blue
Jays involve a number of components, including fixed and moving aspects of the head, body, wings, legs, and plumage.
In birds movement of conspicuous parts of the entire body, as well as the plumage may be important in displays (Tinbergen,
19'+8), and in addition, the position and degree of piloerection of various parts of the plumage may have specific communicative significance (Morris, 1956). Many of the visual displays of the Blue Jay have the same physical characteristics as functionally similar displays that have been described in other avian species (Armstrong, 19^7)*
Maintenance Postures
Blue Jays engaged in such maintenance activities as feeding and resting keep the plumage relaxed and the body in a neutral position or one suited to the activity at hand.
During water and sun bathing the feathers are ruffled to facilitate wetting or warming (by the sun). Maintenance Ik-0 141 postures require little comment, as they are essentially identical to those described for most species of birds.
Agonistic Postures and Displays Postures and displays of Blue Jays involved in aggressive or sexual activities have many features in common. Most of the aggressive and sexual signals involve some degree
of piloerection, especially of the crest. Erection of plumage effectively increases the size of the displaying bird
(Dilger, 1956). Erection of the crest alone does not signal
a threat; however, when it is combined with a lowering of the
head and/or partial opening of the mandibles, aggression is
signified. As the degree of aggression increases, other
components are brought into play. The degree of piloerection
increases, the wings and tail are held open or flicked open
and closed and the body is tiptoed. These components further increase the conspicuousness of the bird because they involve
motion, increase in effective size, and display of
conspicuous markings.
The posture of a highly aggressive bird (Fig. 6) is
very similar to that of a sexually excited bird (Figs. 10, 11
and 12), suggesting a common origin for the two types of
display. Fanning of the wings and tail and raising of the
tail are thought to have been derived from the flight
intention movement (Daanje, 1950). Erection of the plumage
during courtship is probably derived from aggressive displays; 142 however, it serves a similar function, increasing the effective size of the bird. There are distinct differences between intense aggression postures and courtship displays that probably clarify their meaning to the bird at which the display is directed. First, during courtship, the bill is closed and held parallel to the female, whereas in aggressive displays and fighting the open bill is directed toward the object of aggression. In addition, courtship display is accompanied by song, whereas the only acoustic signal that occasionally accompanies aggressive displays is bill snapping.
While sexual displays share many of the components of aggressive displays, they also contain elements characteristic of submissive displays. In avoidance posture the bill is held parallel to or away from the dominant bird, just as the male directs the bill away from the courted female. During courtship bobbing, the male’s bill, at the top of a bob is directed upward. This is reminiscent of the bill-up position of a bird in appeasement posture (Fig. 15)» At the same
time, the head of the male is above that of the female and his throat and belly are exposed. This exposure of vulnerable parts is also seen in appeasement posture and in
the posture of the loser of an aggressive encounter.
It is evident, then, that Blue Jay courtship display, like courtship display in many other avian species
(Armstrong, 19^7), combines elements of both aggressive 1^3 and submissive displays. The elements of aggressive displays
that serve to make the bird conspicuous are present and the elements of submissive displays included signify that the
courting bird does not intend to attack the object of his display. The incorporation of aspects of aggressive and
submissive displays into courtship displays indicates that
courtship behavior is highly evolved behavior, derived from
simpler movements. It is also, in most species, including the Blue Jay, quite stereotyped, supporting the hypothesis
that it develops later than other types of agonistic displays
(Armstrong, 19^7)* Further evidence supporting this
hypothesis with respect to Blue Jay courtship is the
accompaniment of courtship bobbing by song, the most complex
vocalization.
Simple bobbing is a puzzling display to which function
is assigned only with difficulty. The most notable feature
of simple bobbing is the degree of motion involved. I would
like to suggest that the lack of specific components that
might signify aggression, submission or sexual excitement,
indicates that the most important function of bobbing is to lend visual emphasis to vocal displays. As I have mentioned,
bobbing is rarely unaccompanied by vocalization and appears
to be specifically important in distance communication where
gross movement of the body would be the only recognizable
feature of the display. That bobbing is given with a wide
variety of vocalizations, which, themselves, have distinctly 1>+lf different functions, is further evidence that the simple bob is a non-specific signal.
Submissive and Solicitative Postures and Displays
The submissive displays, as a group, are characterized by relaxed or sleeked plumage, upward or horizontal bill point away from the dominant or aggressive bird. The submissive bird usually assumes a position that exposes the throat and belly if the aggressor or dominant is in close proximity. The hunched position of the body, evident in the nestling alarm freeze (Fig. l4), and, to a lesser degree, in avoidance posture (Fig. 13), and sleeked plumage, seen in all of the submissive postures are, in many
respects the opposite of the upright stance, ruffled plumage,
bill forward threat displays. The turning away of the body
and bill from the aggressor is thought to represent the
ritualization of the flight intention movements (Tinbergen,
1959), and probably serves to remove the sign stimuli for aggression.
The solicitative displays are characterized by
crouched body position, lowered head, widely opened b ill and
the fluttering of wings and tail. These types of displays
develop first in very young birds, where they serve to elicit
provision of food by the parents. Later in life adult birds,
especially females, revert to this type of juvenile behavior in courtship feeding and copulation solicitation. Appearance 1^5 of juvenile solicitative behaviors in adult birds is common in many species (Armstrong, 19^7; Andrew, 1961). Such d isp lay s apparently serve two fu n ctio n s : 1) to reduce
aggressive tendencies in the male, and 2) to signal to the male that the female is receptive to courtship feeding and
copulation. Courtship feeding in the Blue Jay serves to establish
a male-feeding-female routine. This is particularly adaptive
in that it allows the female to spend more time incubating the eggs (a strictly female activity), relieving her of the
need to forage for food. Courtship feeding is also important
in the maintenance of the pair bond in Blue Jays. Many of
the captive jays that established pair bonds during their
first breeding season remained paired during the non-breeding
season and into the next breeding season. In these birds
there was considerable reduction or complete absence of the
ritualized male courtship display in the second breeding season. In addition, birds with well-established pair bonds
were ready to nest earlier in their second breeding season.
Thus, courtship feeding is an integral part of the breeding
cycle that permits reproductive activity to be carried out
with maximum efficiency because it reduces the amount of
energy that would otherwise be spent in such activities as
foraging by the female during incubation and renewed
courtship by the male at the onset of each breeding season.
It should be noted that adult solicitative displays 1^6 are accompanied by vocalizations (BK, SK, LK) that resemble food-begging calls of the young (YFB1, YFB2).
The Blue Jay’s repertoire of visual communication signals has a limited number of components that may be combined in different ways to serve different functions. Similar combinations of components (for example, young food-begging and female courtship feeding solicitation) may have other cues that lend them distinctiveness. Thus, two similar visual displays may elicit different responses due to the presence of additional vocal or contextual cues.
Structure, Function and Evolution . of Acoustic Signals
Although the vocal repertoire of the Blue Jay contains only about 20 distinct types of calls, the actual number of meaningful signals is greater because, as with visual displays, a single vocalization may be used to communicate a number of different concepts if it is accompanied by different postures or if it is given in different contexts.
Harmonic Spectra Calls
The'harmonic spectra calls are characterized by numerous harmonics, dominant frequencies of high value, and
long durations. They function as signals of extreme
excitement associated with fear and as contact or location n o te s.
The Distress Call (DC) has the characteristics of a
sound that can be located only with difficulty (Marier, 1955? i4y
Bremond, 1963), that is, it is long, begins and ends imperceptibly, and its dominant frequencies are rather high and stable throughout the call. The DC can be said to be a warning of imminent danger in that the bird giving the call has already been caught or is being closely pursued. It probably elicits a flight response in other jays, although I have not been able to test this hypothesis to my satisfaction.
A similar DC in the European Jay has been described (Bremond,
1963). The Alarm Call (AC) is also a signal of imminent danger, although its abrupt changes in frequency at the beginning and end make it somewhat easier to locate. However, it is a long call with a dominant frequency that is rather high. Hardy (1961) and Edwards (1971) have both described this call and suggested that it serves as an alarm call, and
Brown (196*+) describes an alarm call in Steller’s Jay that is similar in structure to the Blue Jay AC.
The Flock Contact Call (FC) has only one characteristic that would make its source easily locatable—the presence of very pronounced frequency modulation (FM) at its end. However, the FC is repeated very frequently and this probably accounts for its function as a contact note. It is also accompanied by simply bobbing, which lends visual conspicuousness to the caller. Edwards (1971) concurs that this call, to which he gives the name "monotone waa" call, serves as a flocking call. 148 Type 1 and Type 3 Young Food-begging C alls (YFB1,
YFB3) are easily locatable calls due to short durations, abrupt changes in frequency, and/or low values of dominant frequencies. On the other hand, YFB2 and YFB4 provide few
cues for location in that they are of long duration and end indefinitely. YFB1 and YFB2 are given by nestlings or very young fledglings, while YFB3 and YFB4 are given by older nestlings and fledglings. Thus, although the calls given change with age, there are calls that can be located both with and without ease used by a young bird of any age. I
have not ascertained how young birds might decide which type
of call to use, but it seems likely that they may take cues
from the behavior of their parents.
The Keu calls are all different types of contact
notes used by pairs and family groups. The Begging Keu Call
(BK) and the Soft Keu Call (SK), used as proximal communication signals, are frequently repeated, but the Loud Keu Call (LK)
is not. The LK has more pronounced changes in inflection and
is usually quite loud, unlike the BK and SK. Thus, all these
contact calls provide good location cues, but in different
fashions. Goodwin (1952) describes a call similar to the SK in the European Jay that is used by the male to call the
female to a nest site he has chosen. Hardy (1961) and
Edwards (1971) both suggest the Keu calls to be important
v o c aliz atio n s in communication between members of a p a ir . The Crow C all (CC) and the Meow C all (MC) are both
examples of vocal mimicry, a phenomenon that has been 1>+9 described in Blue Jays (Visher, 1912; Edwards, 1971)* Whether or not these calls serve any specific functions is unclear at present. Because the harmonic spectra calls share so many physical and functional sim ilarities and because they are
quite similar to the calls of other jays (Hardy, 1969), it seems reasonable to hypothesize that they were all derived
from one basic type of call. This call, in its primitive
form, was probably rich in harmonics with a low fundamental
frequency (F), and little or no inflection. Slight changes
in duration, in F, either by inflection or modulation,
combined with the additional behavioral cues afforded by
combining postures and displays with acoustic signals, may
have become stable over time, provided they were adaptive, allowing the development of an increased number of specific sig n a ls .
The Pumphandle Calls
The pumphandle calls are higher in frequency and
shorter in duration than most of the harmonic spectra calls.
They have few harmonics and, unlike harmonic spectra calls,
the F is always the dominant frequency. Pumphandle calls
function as territorial calls, alert calls and expressions of
excitement associated with uncertainty or potentially
threatening situations. The harmonic spectra calls function as contact notes and are locatable mainly by virtue of
frequency of repetition and by abrupt changes in frequency 150 over short time periods (slurs). The pumphandle calls, on the other hand, usually involve distance communication and are locatable by appropriate features: purity of tone, abrupt starts and stops, and clear, sharp, unslurred frequency changes. The Bell Song (BS) is mainly a territorial call, but it is also an alert signal or expression of excitement usually concurrent with the presence of strange, possibly dangerous, objects or organisms in the environment. Of all
the calls in the repertoire of the Blue Jay, the BS is the purest in tone. This purity of tone, in combination with a relatively low F and abrupt start, stop and frequency change,
account for the fact that j.t carries well over long distances
(Bremond, 1963). As a territorial call the BS is often
accompanied by simple bobbing from a conspicuous location
(treetops, etc.), affording a visual cue to facilitate
location of the caller. As an alert call the BS is often
given with the investigatory posture, which is actually more
an expression of the behavioral state of the bird that can
be interpreted as such by a proximal observer, than it is a
distance location cue. Hardy (1961) and Edwards (1971) have described the BS as a territorial call and Brown (196^)
described the structurally similar "musical call" of the
Steller's Jay as a territorial call.
The Wheedle B ell Song (WBS) functions m ainly as an expression of uncertainty. The start and stop portions of 151 the call are less abrupt than those of the BS and the WBS is usually given at a slightly lower volume. Thus it is somewhat more difficult to locate; however, it is often given when
birds are in groups and may be accompanied by simple bobbing
or investigatory posture, both of which lend it some visual
conspicuousness.
The C lick C alls The click calls are usually intermediate between
harmonic spectra calls and pumphandle calls with respect to
dominant frequency values. They have few harmonics,
pronounced changes in inflection over relatively long time
spans and, of course, clicks. The click calls are usually
given at rather low volume, but are easily locatable by
virtue of their structure. All of the calls may serve as
alert notes. They may also express excitement associated
simultaneously with fear and frustration. One call, the
Triple Descending Whistle (TDW), is sometimes a territorial
or victory announcement call.
I observed the Rolling Click (RC) to be given only by
females as did Amadon (19*+^) and Edwards (1971); however. Hardy (1961) reported that he heard this call from both sexes. Because the call is probably limited to females, one would
expect it to be given in sexual contexts or, at least, in
relation to a specifically female activity. While Edwards
(1971) reported this to be true, I have not. When the RC was
not given as an alert call, it seemed to indicate frustration 152 due to a thwarted drive to flee. Edwards (1971) mentioned
that females giving the RC in a sexual context may have been in conflict situations, specifically a conflict between
drives to flee from or attack the male as he approached. These circumstances show some similarity to those in which I observed the RC. The extremely abrupt character of the RC, in addition
to its exclusive association with bobbing, make it an obvious, easily locatable signal.
The Descending Whistle (DW) functions mainly as an
alert signal or as an expression of excitement generated by
the situation which prompts the alert signal. The voiced
sound in the DW is more obvious than that in the RC and covers
a much wider frequency range. This tends to overpower the
abruptness of clicks and the caller is thus less easily
located. DW calls, however, are associated with lower levels of excitement.
The fu n c tio n of the Growl (GR) is u n c le a r. I t is
given randomly by birds in a relaxed behavioral state and
perhaps merely serves as an expression of that condition.
The TDW is the only other territorial call besides the BS. It is given at a lower intensity than the BS, brt is
fairly pure in tone and is characterized by slow, slurry
frequency changes. The voiced sound in the TDW overpowers the clicks almost entirely. Because this call is sometimes
given by the winner of an aggressive encounter, it may 153 function as a defense of small, mobile territories such as individual distance, mates, temporary perches and feeding stations rather than territory in the usual sense (nesting territory). The "musical call" of the Steller's Jay (Brown,
196*+), which is structurally similar to both the BS and the
TDW, is often given during conflicts between males. This same call in the Steller's Jay is also a territorial call similar in function to the BS.
The pumphandle and click calls are more similar to each other in structure and function than they are to the harmonic spectra calls. This suggests that they may have evolved from a single primitive call characterized by purity of tone, absence of harmonics, and abruptness in changes of frequency. Many of the calls in these groups function as alert signals or expressions of mild excitement generated by potential rather than imminent danger. In addition, one call from each group is used as a type of territorial call.
Simple pure tone calls of similar function are found in other New World jays (Hardy, 1969), but the variety of calls seen in the Blue Jay repertoire is not present in most cases. A number of corvids have a rattle call similar to the
RC (Amadon, 1944, Hardy, 1961, Sutton and Gilbert, 1942).
I would like to suggest that the calls developed from
the primitive pure tone type call (pumphandle and click calls) were enhanced by the combination of clicks with pure cone calls. Thus, there is a spectrum of calls ranging from a 15^ pure tone whistle with no clicks (BS) to a call in which loud, regular clicks dominate the voiced sound (RC).
It is difficult to speculate whether a primitive
click call arose independently and was later combined with pure tone calls or whether clicks arose as a "by-product" of
increases in abruptness of frequency changes over shorter and
shorter time periods.
Song The principal function of song in the Blue Jay is as
an accompaniment to male courtship bobbing. It is very
musical in quality and highly variable in structure. Although
song is always given at a very low volume, it can be easily
heard by the female who is rarely less than a meter away from
the male during courtship. Brown (196^) describes a
vocalization comprised of whistle-like tones and gutteral
sounds that is given by the male Steller's Jay as he circles
and sidles up to the female.
Secondarily, song functions as an indicator of an exceedingly relaxed behavioral state. Structurally similar
vocalizations have been described in the Mexican Jay (Brown,
1963a), the Gray Jay (Lawrence, 1957)? the European Jay and Lanceolated Jay (Garrulus lanceolatus), respectively
(Goodwin, 1952). All of these authors report that the vocalization is given randomly by birds in relaxed conditions. Lawrence (1957) suggests that the vocalization, in such a context, constitutes displacement behavior. 1 do not believe 155 this is true of Blue Jay song because there is no evidence of drive conflict in the behavior of singing birds. In conclusion, both the visual and vocal communication signals of the Blue Jay appear to have origins in simple, stereotyped behavior patterns. Most of the visual displays appear t,o be derived displays, that is, they are ritualized patterns derived from simple fight or flight intention movements.
The vocal displays appear to have arisen from two or three, at most, primitive types of calls. The first type, from which harmonic spectra may have developed, was probably an alarm call rich in harmonics, with a high dominant frequency that showed little change throughout the duration of the c a l l . The second type was probably a t e r r i t o r i a l c a l l , pure in tone with a low, abruptly changing dominant frequency. Clicks may have arisen as the frequency changes within the call retained their abruptness but occurred in a shorter time span, or they may have been present as a distinct acoustic signal that was later combined with pure tone calls.
Evolution of communication signals in the Blue Jay shows a trend toward variety, rather than complexity. Only one visual display (courtship bobbing) and one vocalization
(song) show a high degree of complexity. Instead, a wide variety of vocal and visual signals has developed. The large number of contextually modifiable combinations of both types of signals renders the Blue Jay's repertoire of communication signals quite extensive. CHAPTER VI
SUMMARY
Visual and acoustic communication signals in the Blue Jay, Cyanocitta cristata, were studied in a population of 25 captive, hand-raised birds and "in the field." Observation, analyses of 16mm films, and sonagraphic analyses of recorded calls were used to elucidate the physical and functional characteristics of signals.
Blue Jays exhibit about 20 distinct visual communication signals. The function of a given signal is determined by the context in which it is given, as well as fixed or moving aspects of "facial expression," head position,
body position and piloerection. Movement in general, as well
as movement of s p e c if ic , o fte n v is u a lly conspicuous, p a rts of
the body or plumage, probably serves to give visual emphasis
to displays, often without changing their meaning, just as an increase in volume might emphasize an acoustic signal.
Visual communication signals may be placed in three groups on the basis of the functional and physical
similarities they demonstrate. The first group of postures, which do not appear to function as communicative signals, are
156 157 those assumed during maintenance activities. They are characterized by relaxed or fluffed plumage, neutral body position, appressed wings, and closed tail. The second group is characterized functionally as primarily agonistic and is associated with erection of body, and, especially, head plumage and abrupt movements, if any, of wings and tail. The last group of displays functions as submissive or solicitative signals and is associated with sleeking of head and body plumage and fluttering type movements of the wings and t a i l .
Most of the visual displays appear to be derived displays, that is they are ritualized patterns derived from simple fight or flight intention movements.
Twenty different types of vocalisations in the Blue Jay's acousti c repertoire are described. Analyses revealed that the calls may be placed in four distinct groups on the basis of gross physical characteristics and functional sim ilarities. Within groups the calls differ structurally from each other with respect to the number of sound sources, fundamental and dominant frequencies, inflection, and the
occurrence and nature of frequency modulation. The biological significance of a call is determined by its physical structure, the visual displays with which it may be
associated, and the behavioral context in which it is given.
The harmonic spectra calls are rich in harmonics, high in dominant frequencies and long in duration. They 158 function as indicators of alarm, frustration and excitement associated with fear. They are also used as contact notes.
The pumphandle calls have few harmonics, strong frequency modulation, and low dominant frequencies. They indicate mild excitement and uncertainty, and they also serve as territorial or alert calls. The click calls have harmonics, clicks, strong and regular frequency modulation, and terminal downward in f le c tio n . They express excitem ent a sso c ia te d w ith both frustration and fear. Song is highly variable in physical characteristics and is the principal vocalization of the courting male. It is also given randomly by birds in a calm behavioral state.
That vocalizations fall into distinct structural groups, which, within themselves, demonstrate functional cohesiveness, suggests that diversification from two or three primitive call types has occurred. Evolution of communicative signals in the Blue Jay shows a trend toward variety, rather than complexity. The combination of visual with vocal signals enhances the repertoire of communicative s ig n a ls . LITERATURE CITED
Amadon, D. 19’+^* A preliminary life history study of the
Florida Jay, Cyanocitta c.. coerulescens. Results
Archibold Exped., No. 50. Amer. Mus. Novitates, No. 1252: 1-22.
Andrew, R. J. 1961. The displays given by passerines in
courtship and reproductive fighting: a review. Ibis 1033 :315-3^8, 5^9- 597* Armstrong, A. 19^7- Bird display and behavior. Lindsay Drummond L td ., London. 4-31 p.
Bent, A. C. 1946. Life histories of North American jays,
crows, and titmice. U.S. Natl. Mu.r. Bull. 191,
pp. 32-52.
Berger, A. J. 1961. Bird study. John Wiley and Sons, Inc.,
New York, xi + 389 pp.
Bremond, J. C. 1963* Acoustic behavior of birds, pp.
695- 750. IN: Busnel, R. G. (ed.) Acoustic behavior of animals. Elsevier Publ. Co., New York, xx +
933 pp. Brown, J. L. 1963a. Social organization and behavior of the
Mexican Jay. Condor 65:126-153*
159 160 Brown, J, L. 1963b. Aggressiveness, dominance and social organization in the Steller Jay. Condor 65:^60-^-8'+. Brown, J. L. 196^. The integration of agonistic behavior in
the Steller's Jay Cyanocitta stelleri (Gmelin). California Univ. Publ. Zool. 60:223-328.
Chamberlain, D. R., and G. W. Cornwell. 1971. Selected
vocalizations of the Common Crow. Auk 88:613-634-.
Daanje, A. 1950. On locomotor movements in birds and the
intention movements derived from them. Behaviour
3:48-99. Davis, L. I. 1964. Biological acoustics and the use of the
sound spectrograph. Southwestern Nat. 9:1l8-l45.
Dilger, W. C. 1956. Hostile behavior and reproductive
isolating mechanisms in the avian genera Catharus and
Hylocichla. Auk 73:313-353* Edwards, R. F. 1971* Vocalization and its ontogeny in the Blue Jay (Cyanocitta cristata). M.S. Thesis,
Southern Illinois Univ., Carbondale.
Goodwin, D. 1952. A comparative study of the voice and some
aspects of behavior in two Old World jays.
Behaviour: 293-316.
Gross, A. 0. 1949. Nesting of the Mexican Jay in the Santa
Rita Mountains, Arizona. Condor 51:241-249.
Hardy, J. W. 196I. Studies in behavior and phylogeny of
certain New World jays (Garrulinae). Univ. Kan. Sci.
Bull. 42:13-149. 161 Hardy, J. W. 196^. Behavior, habitat, and relationships of
jays of the genus Cyanolyca. C. C. Adams Center for
Ecological Studies, Occas. Pap. 11:1-1^. Hardy, J. W. 1969- A taxonomic revision of the New World jays. Condor 71:360-375.
Hinde, R. A. 1966. Animal behavior. McGraw-Hill Inc., New
York. X + 53^ pp. Lawrence, ¥. D. 1957* Displacement singing in a Canada Jay
(Perisoreus canadensis). Auk 7^:260-261.
Marier, P. 1955- Characteristics of some animal calls.
Nature 176:6-8.
Miskimen, M. 1951. Sound production in passerine birds. Auk
68:^-93-50^. Morris, D. 1956. The feather postures of birds and the
problem of the origin of social signals. Behaviour
9: 75 - 113. Sutton, G. M., and P. W. Gilbert. 19^2. The Brown Jay's
furcular pouch. Condor 44:160-165.
Sutton, G. M. 1967 . Oklahoma birds. Univ. Oklahoma Press,
Norman. x lv + 674 pp.
Tinbergen, N. 1948. Social releasers and the experimental
method required for their study. Wilson Bull. 60:
6-51 .
Tinbergen, N. 1959. Comparative studies of the behaviour of
gulls (Laridae): a progress report. Behaviour 15: 1-70. 162 V isher, S. S. 1912. Blue Jay im ita tin g song of Brown
T hrasher. Condor '+:199* APPENDIX
Symbols Used in the Dissertation
AC The Alarm Call (Fig. 19).
AM Amplitude modulation—changes in the amplitude of a
vocalization.
BK The Begging Keu Call (Fig. 27).
BS The Bell Song (Fig. 33).
CC The Crow C all (Fig. 30).
DC The Distress Call (Fig. l 8).
DW The Descending Whistle (Fig. 37).
F The fundamental frequency of a vocalization or one of
its sound sources, that is, the frequency with the lowest value.
FC The Flock Contact C all (Fig. 20).
FM Frequency modulation—changes or warbles of the fundamental frequency.
GR The Growl (Fig. 38).
HI, H2, etc. The first harmonic, second harmonic, etc. LK The Loud Keu Call (Fig. 29).
MC The Meow C all (Fig. 31 ).
RC The R ollin g Click C all (Fig. 36).
163 164-
81 One of the sound sources (the first described for each call in the text) of a vocalization.
82 The second sound source described for a vocalization
in the text. 8K The 8o ft Keu C all (Fig. 28).
88 A sound so urce—one of two sounds th a t can be
produced by a Blue Jay. TDW The T rip le Descending W histle (Fig. 39).
WB8 The Wheedle B ell 8ong (Fig. 35).
YB8 The B ell 8ong of young Blue Jays (Fig. 34-).
YFB1, YFB2, etc. The Food-begging Call of young Blue
Jays, Type 1 ; Type 2, etc. (Figs. 23 - 26).
YFC The Flock Contact Call of young Blue Jays (Fig. 22).